The present invention deals generally with pipe inspection, and more specifically with inspection of the internal cross-sectional shape of pipes.
Sewer pipes placed underground may be partially collapsed or deflected under the weight of soil or other loads. Such pipes, typically having a round cross-sectional shape when not deformed, become unsatisfactory when they are deformed too much. Various government ordinances require inspection of such pipes to ensure deflection does not exceed, for example, 5 percent. This problem of deflection is especially present with certain types of pipes, such as polyvinyl chloride (PVC) pipes, popular for selected applications.
Accordingly, sewer pipes need to be inspected to ensure that they have not unduly deformed or collapsed. Various methods presently exist for conducting such inspections which, in my typical experience, require a crew of four persons to inspect about 3,000 linear feet of sewer pipe per workday. The present invention allows for more than a four fold increase in productivity, requiring only two persons to inspect about 7,000 linear feet of sewer pipe per day.
Prior sewer inspection techniques involve pulling a mandrel by a chord through the pipe to be inspected. However, prior to pulling the mandrel through the sewer pipe, the inspectors have to thread the chord through the pipe ahead of the mandrel. This threading is done in a variety of manners, including directing an electric toy car with a string attached thereto through the pipe, floating a buoyant device with a string attached thereto down the sewer pipe, or blowing a parachute with a line attached thereto down the pipe with an air compressor. After this initial line is thread down the pipe, an operator at the downstream end of the sewer pipe pulls the mandrel through the pipe until a point where a deformation is encountered. These techniques require the labor intensive step of initially threading the line down the sewer pipe before the mandrel can even be run through the inspection. This requires having personnel at both the upstream and downstream ends of the pipe which is being inspected.
U.S. Pat. No. 2,782,370 discloses a device which has two members which both travel down a pipe for detecting electrical current irregularities which evidence potential corrosion leaks.
U.S. Pat. No. 4,354,379 discloses a device for testing the roundness of oil well pipe segments by projecting, under air pressure, a free floating drift through the pipe. U.S. Pat. No. 4,354,379 alternatively discloses the conventional approach discussed above of pulling the drift through the pipe using a cable in front of the drift.
The present invention provides a unique combination particularly well-suited for inspecting underground pipes such as sewers. The present inventive method may be conducted either from the upstream end of the pipe to be inspected or from the downstream end. The inventive method is rapid and efficient compared to prior methods. Particularly, a specially adapted mandrel is inserted into the pipe. The mandrel has a retrieval chord attached to it which trails behind the mandrel and which is preferably wound up on a reel. A plug member is fixed in the pipe behind the mandrel. A pressurized fluid, such as compressed air, is then forced in the space between the plug and the mandrel, propelling the mandrel along the pipe away from the plug. The mandrel is advanced as much as five hundred or more feet, trailing the retrieval chord behind it as it advances. After the mandrel has advanced the full length of the pipe to be inspected without stopping at a deformation, the mandrel is removed at the next manhole. If the mandrel stops before reaching the next manhole at a sufficiently small deformation in the pipe, the pressure is turned off and the mandrel is retrieved by pulling on the retrieval chord. As stated above, this technique may provide as much as a four fold increase in productivity, and is a significant advance in the art.